6533b839fe1ef96bd12a5999

RESEARCH PRODUCT

a1(1420) peak as the πf0(980) decay mode of the a1(1260)

subject

description

We study the decay mode of the ${a}_{1}(1260)$ into a ${\ensuremath{\pi}}^{+}$ in $p$ wave and the ${f}_{0}(980)$ that decays into ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ in $s$ wave. The mechanism proceeds via a triangular mechanism where the ${a}_{1}(1260)$ decays into ${K}^{*}\overline{K}$, the ${K}^{*}$ decays to an external ${\ensuremath{\pi}}^{+}$ and an internal $K$ that fuses with the $\overline{K}$ producing the ${f}_{0}(980)$ resonance. The mechanism develops a singularity at a mass of the ${a}_{1}(1260)$ around 1420 MeV, producing a peak in the cross section of the $\ensuremath{\pi}p$ reaction, used to generate the mesonic final state, which provides a natural explanation of all the features observed in the COMPASS experiment, where a peak observed at this energy is tentatively associated to a new resonance called ${a}_{1}(1420)$. On the other hand, the triangular singularity studied here gives rise to a remarkable feature, where a peak is seen for a certain decay channel of a resonance at an energy about 200 MeV higher than its nominal mass.